Since molded articles prepared from a synthetic polymer molding material are usually significantly hydrophobic, they have a property that they tend to store a static electrical charge. The articles attract dust due to a static charge, and the static charge can cause electric shock, ignition, and the like. Consequently, the charging of the articles makes them difficult to use.
In order to prevent the charging of synthetic polymer material molded articles, it has heretofore been conducted to knead an electrically conducting agent such as carbon black and or a conductive metal powder, a surfactant, and the like into the polymer material, or to coat the molded articles with such antistatic agents. For example, Japanese Unexamined Patent Publication (Kokai) No. 63-307947 discloses a film coated with a charge-transfer complex. However, when resin molded articles, to which desired antistatic properties are imparted by using an electrically conducting agent such as a charge-transfer complex, is to be obtained, the amount of the conducting agent to be used becomes large, and other properties of the molded articles thus obtained tend to be deteriorated. Moreover, there is also a method of imparting antistatic properties to resin molded articles by adding a charge-transfer complex to an organic polymer. However, when the method is adopted, preparing molded articles having excellent transparency becomes difficult because the compatibility of the charge-transfer complex and the organic polymer is insufficient. Moreover, a large amount of an electrically conducting agent must be used to obtain a product having desired antistatic properties. Consequently, there arises the problem that the molded articles thus obtained have deteriorated properties.
In contrast to the electrically conducting agent, antistatic agents which are mainly surfactants have the advantages that many kinds of antistatic agents are known to exist, and that suitable ones can be selected so that their properties are in accordance with desired properties. Of these antistatic agents, internal addition type agents which are used by kneading them into a polymer material are disclosed in Japanese Unexamined Patent Publication (Kokai) No. 63-314261. Although such type antistatic agents have excellent antistatic properties, they have the disadvantage that satisfactory antistatic properties cannot be obtained when they are used by adding them to coating materials. On the other hand, a coating material of coating type which is applied to the surface of polymer material molded articles to impart antistatic properties thereto cannot impart sufficient antistatic effects in low humidity conditions. Moreover, the coating material may lose its antistatic effects during a drying step after the molded articles are coated therewith, during treatment such as heating, rubbing and cleaning at the time of subjecting the coated molded articles to drawing, thermosetting, shaping by heating or the like procedure, and the durability often becomes unsatisfactory.
As measures for solving such problems, Japanese Unexamined Patent Publication (Kokai) No. 63-6064 discloses the use of a coating material to which a phosphoric acid ester is added, and Japanese Unexamined Patent Publication (Kokai) No. 2-186598 proposes the use of a coating material to which a fluoro compound is added. However, even polymer material molded articles coated with a coating material containing these antistatic agents do not have well balanced mechanical strength of the coating thus formed, durability of the antistatic properties, and the like, when subjected to a long term durability test such as a humidity test.
Furthermore, a method of coating molded articles with an UV-curable coating material, and curing the coating material has been known. The method has the advantages that the substrate can be selected from a wide range of materials because the coating thus formed is excellent in adhesion to the substrate, and that the treatment time for forming the coating thereon is short. In addition to the advantages, the method has the advantage that the method can form a coating excellent in various coating properties such as chemical resistance, scuff resistance and abrasion resistance. However the coating has the problem that it generates a static charge due to friction, etc., and as a result dust tends to adhere thereto.
Furthermore, since the quantity of information processed in a computer, etc., has been increased in recent years, the memory capacity for recording signals in an optical disk has been increased, and the signal information density is very high. Consequently, the optical disk must be produced by molding with high precision. However, the conventional acrylic UV ray-curable coating material has the disadvantage that it suffers curing shrinkage during the formation of a coating layer and the disk warps. In order to overcome the problem of the curing shrinkage of the coating layer, investigation has been carried out into the reduction of the stress applied to the disk by decreasing the coating layer thickness, and the diminishing of the curing shrinkage by adding a polymer to the coating material. However, these procedures have disadvantages. For example, in the former procedures control of the coating layer thickness is difficult, and the mechanical strength of the coating thus obtained becomes insufficient. On the other hand, in the latter procedure, the coating solution becomes highly viscous, and the adhesion of the coating is lowered. Consequently, it is difficult to obtain a desired performance of the coating layer. In view of the problems described above, the development of a coating material showing a decreased curing shrinkage, having a low viscosity and excellent in a balance between the antistatic properties and the adhesion of the coating is desired.